Information can be represented as signals in numerous manners. One such manner is modulation, in which information is encoded by varying the properties of a carrier signal. One example of modulation is amplitude modulation (AM) employed in AM radios. In an AM radio signal, an amplitude of a signal at a fixed frequency is varied over time according to the information to be conveyed. Another example of modulation is pulse width modulation (PWM). Pulse-width modulation (PWM) is frequently used in electronic devices and telecommunications, such as mobile phones, to transmit information from one point to another point, whether that is across a circuit board or across miles of airwaves. Pulse-width modulation (PWM) encodes data as a series of pulses in a pulsing signal. The pulses are generated by a circuit, such as the one illustrated in FIG. 1.
FIG. 1 is a circuit schematic showing a conventional pulse-width modulator. A modulator 110 may include switches 116 and 118 coupled to positive and negative power supplies, respectively. The switches 116 and 118 may be configured to drive an output node 102 when coupled to node 112 and not drive the output node 102 when coupled to node 114. Control signals CTRL1 and CTRL2 supplied to switches 116 and 118 may couple the switches 116 and 118 to node 112 to generate pulses at the output node 102. For example, an average zero output may be generated by applying the control signals illustrated in FIG. 2A to the switches 116 and 118 of FIG. 1. A first control CTRL1 signal 202 and a second control CTRL2 signal 204 may be high at time 212 to couple the switch 116 to node 112 and the switch 118 to node 114. At time 214, the switches 116 and 118 reverse such that switch 116 is coupled to node 114 and switch 118 is coupled to node 112. As another example, an average positive output may be generated by applying the control signals illustrated in FIG. 2B to the switches 116 and 118 of FIG. 1. A first control CTRL1 signal 206 may go high at time 212, followed by a second control CTRL2 signal 208 at time 216. Now, the output at output node 102 is an average of the strength of the drive from switches 116 and 118 but weighted by the amount of time that each of the switches is coupled to the node 112. When the drive from switches 116 and 118 is equal, the output at output node 102 is a positive pulse between time 212 and time 214, because the first control CTRL1 signal causes the switch 116 to be coupled to node 112 for a longer duration that control CTRL2 signal causes the switch 118 to be coupled to node 112.
In the pulse-width modulation (PWM) technique described above with reference to FIG. 1, the output at output node 102 is not a perfect signal. Noise is generated by the power supplies for the switches 116 and 118, and that noise becomes part of the output at output node 102. One type of noise introduced by the switches 116 and 118 is thermal noise. Thermal noise is variations in the driving of the node 112 that occur as a result of thermal fluctuations within the power sources for the switches 116 and 118. The thermal fluctuations may be due to environmental changes or heat produced by operating the power sources. In conventional pulse-width modulation (PWM) techniques described above, thermal noise is always present in the output signal because the switches 112 and 118 are never both coupled to node 114. Instead, one of the switches 116 and 118 is always driving the output node 102.
As electronics continue to advance, the total power consumed by the devices is reduced resulting in large problems with noise. The power consumption reduction is often due to a decrease of the magnitude of the supply voltages of the electronics necessitated by a shrink of the transistors that are the building blocks of the electronics. The sources of noise, such as thermal noise in power supplies, does not necessarily decrease along with the power consumption. Thus, the relative contribution of noise to the output signal increases as power consumption decreases. Because many applications require a sufficient signal-to-noise ratio (SNR), the noise introduced by the power sources is a problem when a signal level is small.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for pulse-width modulators employed in consumer-level devices, such as mobile phones. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art.